ddk 2.0.0-rc.1

application tooling for DLCs 🌊
Documentation 
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//! Splice (DLC) funding input construction.
//!
//! A splice reuses the 2-of-2 funding output of a previous, on-chain DLC as an
//! input to a new contract's funding transaction (this is how rollovers and
//! collateral changes are expressed). [`create_dlc_splice_input`] rebuilds that
//! output from the previous contract's offer and accept messages, so callers
//! never have to supply raw transaction data.
//!
//! Only the offering party may contribute a DLC input; the accepting party's
//! funding inputs must be ordinary wallet UTXOs.

use bitcoin::ScriptBuf;
use ddk_messages::{AcceptDlc, DlcInput, FundingInput, OfferDlc};

use super::accept::create_dlc_transactions;
use super::context::contract_id_from_transactions;
use super::error::ContractError;
use super::types::{random_serial_id, Party};

/// Maximum witness length reported for a DLC (2-of-2 P2WSH) funding input.
///
/// Must exceed 108 so that [`ddk_dlc::create_spliced_dlc_transactions`]
/// separates DLC inputs from ordinary P2WPKH wallet inputs. The value matches
/// `ddk-manager`, so a stateful counterparty rebuilds an identical funding
/// transaction.
pub const DLC_INPUT_MAX_WITNESS_LEN: u16 = 220;

/// Builds a splice (DLC) funding input from a previous contract's messages.
///
/// The previous contract must be the funded DLC whose 2-of-2 funding output is
/// spent into the new contract. `local_party` identifies which side of the
/// previous contract the *new offering party* was; offer-only splicing uses
/// [`Party::Offer`].
///
/// The returned [`FundingInput`] carries the previous funding transaction, its
/// funding output index, and a [`DlcInput`] with both prior funding public keys
/// and the prior contract id. Place it in the offering party's funding inputs
/// when building the new offer. Signing it later additionally requires the
/// prior contract's funding secret key (see
/// [`sign_accept_spliced`](super::sign_accept_spliced) and
/// [`finalize_sign_spliced`](super::finalize_sign_spliced)).
pub fn create_dlc_splice_input(
    prev_offer: &OfferDlc,
    prev_accept: &AcceptDlc,
    local_party: Party,
    input_serial_id: Option<u64>,
    max_witness_len: u16,
) -> Result<FundingInput, ContractError> {
    if max_witness_len as usize <= 108 {
        return Err(ContractError::InvalidFundingInput(
            "DLC input max witness length must be greater than 108".to_string(),
        ));
    }
    let transactions = create_dlc_transactions(prev_offer, prev_accept)?;
    let fund_vout = transactions.get_fund_output_index() as u32;
    let contract_id =
        contract_id_from_transactions(&transactions, &prev_offer.temporary_contract_id);
    let (local_fund_pubkey, remote_fund_pubkey) = match local_party {
        Party::Offer => (prev_offer.funding_pubkey, prev_accept.funding_pubkey),
        Party::Accept => (prev_accept.funding_pubkey, prev_offer.funding_pubkey),
    };
    Ok(FundingInput {
        input_serial_id: input_serial_id.unwrap_or_else(random_serial_id),
        prev_tx: bitcoin::consensus::serialize(&transactions.fund),
        prev_tx_vout: fund_vout,
        sequence: u32::MAX,
        max_witness_len,
        redeem_script: ScriptBuf::new(),
        dlc_input: Some(DlcInput {
            local_fund_pubkey,
            remote_fund_pubkey,
            contract_id,
        }),
    })
}